RESUMO
The simple arginine binder 1 could be optimized by strengthening pi-cation as well as electrostatic interactions. Electron-donating or -withdrawing substituents in the 5-position provide experimental evidence for pi-cation interactions, because binding energies increase by up to 0.6 kcal/mol due to a single benzene-guanidinium interaction. Even more effective is the introduction of a third phosphonate functionality at the correct distance, so that the guanidinium cation is recognized by optimal electrostatic and hydrogen bond interactions. Monte Carlo simulations and NOESY experiments confirm the expected complex geometries. The optimized host molecule 8 binds arginine half an order of magnitude more efficiently than the parent molecule.
Assuntos
Arginina/química , Difosfonatos/química , Receptores de Aminoácido/química , Difosfonatos/síntese química , Guanidina/análogos & derivados , Guanidina/química , Ligação de Hidrogênio , Cinética , Modelos Químicos , Conformação Molecular , Mimetismo Molecular , Eletricidade EstáticaRESUMO
We present the new host molecule 1 which binds basic amino acid esters in water. It recognizes both positively charged groups of the amino acid esters by electrostatic and hydrogen bond interactions with its four strategically placed phosphonate anions. Selectivity for lysine is achieved by the correct distance between both bisphosphonate pairs. By contrast, the smaller amino acid esters arginine, ornithine, and histidine form 2:1 complexes with 1. In methanol, a double chelate assembly enforced by pi-cation interactions with the imidazolium cation leads to a very high association constant for the 1:histidine complex of 3 x 10(4) M(-)(1).
Assuntos
Histidina/química , Lisina/química , Receptores de Aminoácido/química , Água/química , Ésteres/química , Espectroscopia de Ressonância Magnética , Metanol/química , Modelos Moleculares , SolventesRESUMO
[reaction: see text] We report a number of 1:1 noncovalent complexes composed of a symmetrical trisphosphonate and various symmetrical trisammonium or trisamidinium compounds. The spheroidal complexes show high thermodynamic stability, with association constants Ka reaching 10(6) M(-1) in methanol and in some cases even exceeding 10(3) M(-1) in water. The observed Ka values correlate well with the different degree of preorganization of the complexation partners.
